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Re: can someone explain a little rendering detail?

From: <Irene.Vatton@inrialpes.fr>
Date: Fri, 29 Oct 1999 17:07:14 +0200
Message-Id: <199910291507.RAA00583@tahiti.inrialpes.fr>
To: "Ly, An" <An.Ly@CAI.COM>
cc: www-amaya-dev@w3.org
In-reply-to: Your message of Wed, 27 Oct 1999 11:13:48 -0400."
> Hi all,
> When an element is drawn, its corresponding boxes are processed. Now the
> code in RedrawFrameBottom loops through all planes and renders the boxes in
> their depth order.
> There is code in there that also makes sure that the "dirty rectangle" or
> clipping area intersects the box before it (box) is drawn. My question is,
> how does the rendering system ensure that, if there's 2 boxes (small box
> inside a bigger box), and the bigger box intersects the clipping area but
> the smaller box doesn't, that the smaller box will still be rendered?  Since

A box which intersects the clipping area is rendered. In fact only the part of
box within the clipping area is displayed. If the smaller box is out of the
clipping area, it's not rendered.

> only the bigger box intersects the clipping area, it is redrawn but then if
> it clears the area that it covers, the smaller box inside of it will be
> drawn over. Since the smaller box doesn't intersect the clipping area, it is
> never redrawn.

Normally the clear is also limited by the clipping area. So the smaller box
should not be cleared.

> Even if you put the bigger box in a deeper plane (higher number), the
> rendering doesn't appear to take into consideration that the "background" of
> the smaller box (essentially the bigger box!) has changed, and therefore the
> smaller box, even if it doesn't intersect the clipping area, must be drawn.

I'm not sure that the work is well done, but we planned to take into account 
some boxes have a background to compute the right clipping area.
Did you detected a case where that happens.

> Are there some rules in defining the boxes that prevent the above from
> happening? Should the "smaller" box really have the same dimensions as the
> "bigger" box? Maybe I made a mistake in defining my boxes?

That should work when the bigger box has presentation rules:
Background: color +  FillPattern: backgroundcolor
+ Showbox

> Any help would be appreciated!
> Thanks,
> -An

Received on Friday, 29 October 1999 11:07:24 UTC

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